After the debacle in Yours Truly, Alice and Bob noticed and fixed a vulnerability in their communication protocol. Unfortunately, the signing library they use is third party, so they can't just patch it, and switching to a new one is such a hassle. Can you prove that they really ought to switch to something more secure?
As before, source provided on Alice's remote.
nc puzzler7.imaginaryctf.org 1009
nc puzzler7.imaginaryctf.org 1010
As before, you can append arbitrary data to a signed message. Here's A~Z's excellent explanation of the crypto bits:
That is, you can verify a number of the form g^b * 10^k + c where c and k are controlled constants. With a large enough k, you can set c = - g^b * 10^k mod p + x: alice will parse a number that is congruent to x mod p, for an arbitrary x. Set x = 0, you are done.```